Prior art cold gas dynamic spray systems, sometimes also referred to by the term “cold spray systems”, utilize a spray gun, which is in fluid-tight communication with a nozzle assembly that both directs and acts upon a supersonic gas/powder mixture which is directed at a relatively high velocity and low temperature (compared to other thermal spray processes) to impinge upon a substrate to form a coating. The gas is used as a carrier for the powder that forms a coating on the substrate, and further, as the gas is heated and subjected to temperature and pressure differentials, the carrier gas reaches a velocity that can subject the powder to a thermal and plastic deformation when it impinges upon the substrate to help cause it to adhere to the substrate. While the gas is generally below the melting temperature of the powder, it is subjected to kinetic energy to cause it to be propelled at supersonic conditions to impart sufficient kinetic energy to the powder effluent such that it will adhere to and form a continuous coating on the substrate when it impinges upon it. Given the sophisticated fluid dynamics required for this process, the interior of the nozzle has a precisely machined converging and diverging shape which subjects the powder/gas mixture to a venturi effect as it travels along the nozzle passage.
In general, an electrical heater is used to heat the large volume processing gas. The heater normally heats the gas to as high as 800° C. (1472° F.). The electric heating element, used to heat the process gas, operates under high pressure and temperature environment. During the spraying of some materials such as aluminum, the powder particles get deposited inside the nozzle on the walls blocking the gas flow path. When the nozzle block happens, the gas flow is reduced or even stopped, causing abnormal increase in the temperature and pressure of the heating element and the gun. Such sudden increase in temperature and pressure can damage the gun and the heater, and also affect the safety of the operator.
In the past, such nozzles were made of two halves for ease of fabrication. An advance to this art is shown in U.S. Pat. Nos. 6,502,767, and 6,722,584, issued to the same inventors as the present invention As an improvement, the nozzle was made of a unitary piece of metal. In this design, the nozzle is attached to a 3-5 mm thick washer and this washer is bolted onto the gun body. Some of the issues with this design can be solved by making the nozzle out of a polymer. However, the unitary construction with a converging and diverging internal bore is expensive to manufacture, and the nozzle is typically made with a flange at the end of the nozzle where the nozzle abuts the gun. This construction provides for a relatively straightforward place to join the nozzle to the gun, but as it provides a heat sink in the area behind the diverging section of bore in the nozzle, it allows thermal energy to build there and consequently the nozzle has a tendency to foul or degrade at the higher gas temperature, required for certain coating materials. The present invention provides a nozzle assembly which utilizes a polymer nozzle with a cooling means in the area of the nozzle up stream of the diverging bore section and which has coupling section with a thermal/mechanical design.
The present invention represents a further advance for the use of ultra high temperature alloys (i.e. alloys having melting temperatures of more than about 800° C. (1472° F.). The present invention involves the use of a unitary cylindrical tapered nozzle, which is made, such as by machining, from a single block of a non-metallic material, such as polymer. The interior bore of the nozzle has a precisely shaped converging and diverging taper to induce mixing, velocity and kinetic energy of the powder and gas stream of the spray mixture. In accordance with the present invention, prior art problems with the nozzle when used with particular powders are inhibited. In the past when steel nozzles were used, the taper could become clogged, causing fouling of expensive nozzle, and resulting in down-time for the production apparatus, and possible risk of harm to the gun and heater, substrate and even possibly to workers. In contrast when polymer nozzles are used in the prior art assembly, the nozzles can be subject to thermal degradation in the area at and near the throat of the bore (i.e. where the converging and the diverging areas join). The present invention helps to solve these problems by providing a novel nozzle assembly which includes a polymer nozzle and a thermal/mechanical coupling with a cooling jacket and novel processes which include the nozzle assembly of the present invention to permit superalloys and high temperature alloys to be sprayed onto a substrate.